Electrical transmission



ELECTRI CAL TRANSMI SS ION Filed Sept. 17, 1926 INVENTOR.

Louis C. Billofle, BY I A TTORNEY.

Patented Nov. 3, 1931 UNITED STATES PATXENT OFFICE LOUIS C. BILLOTTE, OImwmm,

M61103 1'0 DEWI'I'I-LA. FRANCE 00., OF CAMBRIDGE, MASSACHUSETTS, A@BPORA'I'IOH-OI' KASSAGHUSETTS mac-121mm.

Application filed September 11, um. Serial r. 130,174.

This invention relates to the transmission and distribution of electriccurrents and voltages and more particularly to the supply of energizingcurrent and voltage to each stage 6 in a multi-stage amplifier of thespace. current ome of the objects of the present invenreduce thedistortion of waves transmitted by a multi-stage amplifier; andgenerally to provide apparatus'adapted for adjustment, to

improve the transmission characteristic of a multi-stage amplifier andto indicate the degree of distortion taking place therein.

i and is connected with In the species of the invention chosen for thepurposes of illustration, a rectifier of alternating current isassociated with a wave suppression filter havin a positive and negativeoutput terminal, a ank of voltage controlresistances being associatedwith the positive terminal of the filter for supplying different stagesof a multi-stage amplifier, while a different bank of voltage controlresistances is so related to a main resistance unit connected with thenegative terminal of the filter as to control the respective grid orcontrol element voltages for the different stages of the amplifier. Themain resistance unit provides a path in com-v mon for the space currentfor all of the tubes all of the cathodes of the tubes.

An. indicator connected between the filter and the banks of resistancesserves to indicate the degree of distortion taking place while thewavesare being amplified, the circuits being adapted for adjustment duringoperation so that the distortion taking place in the amplifier may beminimized. The transmission characteristic ,of the amplifier is furtherimproved by providing a bank of condensers in association with each bankof resistances, the capacity of the condenser assovsecondary providedwith voltage taps 4 which permit of obtaining the desired outputvoltage.

ciated with the positive space current terminal of the last sta of theamplifier being larger than that o the othercondensers in p the samebank.

I These and other objects and featuresof the invention will beunderstood more clearly from the following description and the accompang drawin T e gure in the diagram of a rectifier unit having current andvoltage distributin terminals connected witha multi-stage amp er.

- The alternating current generator 1 or othdrawing shows a circuit ersuitable sourceof. alternating current 13.

connected'with transformer 2 by switch 3, the winding of the transformerbeing The output conductors 5 of the transformer supply alternatingcurrent power to the input terminals 6 of the rectifier network 7 of thefull wave rectifying type made up of rectifier cells 8 poled in suchdirection that the current flows therethrough only as indicated by thearrows. The switch 9, in upper conductor 5, may be opened to include thevariable resistance 10 t erein for controlling the alternating currenttransmitted to the rectifier. The circuit illustrated is adapted forusing electrolytic rectifier cells whichhave their most efiicientvoltage rating below that of the current to be rectified. By placing twoor more of such rectifiers in series so that the sum of their ratedvoltages approximates the voltage to be rectified, it has been foundthat suitable operation takes place, whereas when a single rectifier issubjected to the full voltage, the rectifier deteriorates rapidly andthe rectifying operation fails or is erratic.

The output conductors 11 of the rectifier are connected with the filter12 consisting of the choke coil 13 in series with the upper conductor 11and the condensers 14 and 15 connected in shunt with the conductors 11at'the opposite terminals, respectively, of the choke coil 13. Theinductance of the choke coil shouldbe large, for example, of the orderof henries, or some other suitable value. The filtered direct current istransmitted to the positive terminal 16 and the negative terminal 17 offilter 12, the current transmitted to terminal 16 being transmittedthrough ammeter 19 which is normally short circuited by switch 18.

A main resistance unit 20 connected at one end with the negativeterminal 17 has a'space current return terminal 21. p

- A bank of resistance units 22' has a common connection with thepositive terminal 16. These resistance units are preferably variable,but for the purpose of simplification may be made fixed. In manyinstances it has been found satisfactory to make all but' one of theunits fixed in value and the remainingunit variable to provide anadjustable detector voltage. Each unit has a free terminal 22, 23, 24,25 and 26, respectively, these terminals providing positive potentialconnections for different stages of a multistage amplifier or fordifferent circuits requiring independent voltages.

When employed for supplying space current to a multi-stage ampli er, theresistance units connected with terminals 22, 23, 24, 25 and-26preferably have successively higher resistance values, so that thepotentials of these terminals, when connected with proper anodecircuits, are graded in value from a high voltage to a low voltage inthe order of the terminals named. For example, in a particular instance,a convenient" series of voltages for'certain purposes was found to be135 volts forterminal-22, 90 volts for terminal 23, 67' volts forterminal 24, 45 volts for terminal 25, and a variable-lower voltage forterminal 26. It is to'be understood, however, that the invention is notrestricted to these particular values.

A bank of-condensers 27 has a common connection with terminal 21 ofresistance 20, each c'onnectionwithlow power tubes. 'Condens er 28 maycondenser. v

- A bank of resistance units 29 has a common connection with terminal 17of the main resistance unit 20, this terminal being rendered negative bythe drop of voltage, therein when current is transmitted therethrough toa connected amplifier. Each resistance unit in bank-29 has a freeterminal 30, 31 and conveniently be an electrolytic l 32, respectively,for separately transmitting.

and controlling an auxiliary or grid voltage for each of apluralityofrepeaters 'or amplifiers, as'in-a multi-st'age amplifier. Theseresistance units are preferably variable, but may for the purpose ofsimplification be fixed in value. Preferably, however, at least onevariable unit should be provided when fixed units are employed elsewherein the bank. The resistances are preferably so adjusted or chosen invalue when connected with the control elements or grids of a multi-stageamplifier that higher polarizing voltages are applied to the grids ofthe latter stages of the amplifier than to the first stages thereof.That is, terminal may be more negative than terminal 31, which in turnis more negative than terminal 32 relatively 'to common terminal 21. Inorder to accomplish this result the resistance of the unit connectedwith terminal'30 is less than that of the unit connected with terminal31, which in turn is less than that of the unit connected with terminal32. In the particular instance mentioned above wherein terminal 22 had avoltage of 135 volts, terminal 32 was 4 volts negative, terminal 31 was9 volts negative and terminal .30 was adjustable to a still morenegative voltage adapted for the grid of a power tube in the last stage.

A bank of condensers 33 has a common connection with the free terminal21 of resistance unit 20, each condenser having a free terminalconnected respectively with a separate one of the negative terniinals30, 31 and 32, respectively. Condensers 33 may be of relatively lowcapacity, for example, where a circuit is to be employed with low powertubes, thesecondensers may each have a capacity of the order of one halfa microfarad.

All of the elements described above and numbered 1 to 33, inclusive,are-preferably assembled together as a self contained compactcombination, hereinafter'called a rectier unit or an electric supplyunit, adapted by its terminals 22 to 26 and 30, 31, 32, for

uick andconvenient connection with amplifiersor other loads.

In the circuit shown, a multi-stage repeater or amplifier 34 adapted foruse as a radio receiver, includes the successive stages 35, 36, 37,38,39 and 40, respectivel which may be of the space current type, eachaving an' anode 41 and a filamentary cathode 42 and a grid or controlelement 43. Tubes 35, 36 and 37 serve as radio or high frequencyamplifiers, tube 38 serving as a detector, while tubes-39 and 40 serveasaudio or low frequency amplifiers.

All of the cathodes 42 are connected together with the ground 47, andwith the negative terminal 21 of the rectifier unit by conductors \48and 49. The cathodes or filaments of the tubes 35, 36, 37, 39 and 40 areheated from current from better 44 under the control of rheostat 45, thelament of detector tube 38 bein supplied by battery 44 and controlled byr eostat 46.

The anodes 41 of the first two amplifier stages 35 and 36 are connectedwith terminal 25 which is adapted to supply the lowest amplifiervoltage. The anode of amplifier 37 1s connected with terminal 24 whichsupplies a voltage somewhat hi her than that of terminal 25, and theanode o detector tube 38 is connected with terminal 26 which normally isthe lowest voltage terminal in connection with bank 22 and which ispreferably adjustable to provide the most desirable detector voltage.The anode of audio or low frequency amplifier 39 is connected withterminal 23 which supplies a voltage somewhat higher 4' than that ofterminal 24, the anode of amplifier 40 being connected with terminal 22which supplies the highest voltage.

The grids 43 of amplifiers 35 and 36 are connected with conductor 49 andterminal 21 polarizing potential to the grid ofhigher value than thatapplied to amplifier 37, the grid of poweramplifier tube 40 beiconnected with negative terminal30 whic supplies a suitablyhighpolarizing potential to the grid by adjusting the variableresistance connected with terminal 30. It will thus be seen thatsuccessive amplifying stages are, supplied, with successively higherpositive space current voltages from the terminals 22, 23, 24, 25 and26, respectively, while the grids in successive amplifying stages aresupplied with successively higher negativgpolarizing otentialsrelatively to-the cath es.

accordance with signals or speech are t nsmitted to the input terminals50 of a multi-' stage amplifier circuit by way of antenna" 51 and ground.47 or other suitable means. The

primary winding of input transformer 52 is connected with terminals 50and includes a condenser 53 in circuit therewith for tuning to waves tobe received. Variable condenser 54, in shunt with the secondary windingof transformer 52, permits of tuning the input circuit of amplifier 35to the waves of desired frequency, the amplified'wavesbeing transmittedto the primary winding totransformer 55,'the secondary winding of whichis shunt ed by variable condenser 56 for tuning the input circuit ofamplifier 36 to the same frequenc trans ormers 57 and 58 shuntedrespectively by means of variablecondensers 59 and 60 are. tuned to thesame frequency, so that the desired waves are amplified infthe firstthree stages and-transmitted to the grid of deas that of amplifier 35.Similarly tector 38. The detected waves in the anode circuit of detector38 of audible or low frequency, are transmitted successively through lowfrequenc coupling transformers 61 and responsive device 63.

' Before starting the electrolytic rectifier for the first time, theupper conductor 5 is connected with the lowest voltage tap 4, and switch9 is opened to include variable resistance 10 in the output circuit 5 oftransformer 2, the resistance being adjusted to maximum value beforeapplying current from source. 1 to the primary wlndmg of thetransformer. Switch 3 .is then closed to connect source 1 withtransformer 2 which transmits current is between two taps, connection ismade with the one of higher voltage, switch 9 being kept open'andresistance 10 being adjusted to such a value that the effective voltageapplied to the rectifier is between the voltages of the two taps. I Itis thus possible'to obtain any desired voltage with a relatively smallnumber of taps of the transformer and with a relatively small resistancein series with the transformer output conductors, so that regulation ofthe circuit approaches that obtainable by a direct connectlon with aspecial tap between those actually provided.

Owing to the high electrostatic capacity of p v the electrolyticrectifier cells 8 and the wave Ba '0 or other carrier waves modul ted-insubstantially ree from undesirable wave components.

The total current supplied to amplifie circuit 34 from the rectifier maybe read dir ctly on ammeter 19, by ressing key 18. v

, In general, the ar itrary adj ustment of the positive potentialsof,terminals22 to 26, inclusive, in conjunction with the negativepotentials of terminals. 30, 31 and 32, results in" appreciabledistortion of the wave being amplified, owing to departures of theoperating characteristics of the tubes from the assumed values and thefact that the tubes" do not operate on the most linear portions of theiram-,

plifying characteristics, The effect of the- 7 resulting distortion isto undesirably mutilate the waves transmitted from the amplifier and toproduce distorted sounds in receiver 63. Another efiect is'to change thespace current supplied to the amplifiers so that, when waves of constantamplitude are being ampli- 62 and low requency' amplifiersi39 and 40 ,tothe loud speaking receiver or other suitable fied, a fairly constantchange of deflection may be noted on ammeter 19 with key 18 open, thedegree of distortion being continuously indicated by the amount ofdeflection of the ammeter, as read on its calibrated scale.

When a high frequency wave is being amplified and the amplitude varies,a variable amount of direct current is transmitted through ammeter 19.When the variations of amplitude of the high frequency wave are rapid,the deflection of the ammeter is seemingly constant, owing to itsfailure to respond to the ra id changes of current, but when the rate ofchange of amplitude of the high frequency wave is low, that is, a fewcycles each second, the effect may be readily observed on the ammeter.

In order to adjust the voltages supplied to the amplifier stages tosuitable values to minimize distortion and to insure operation near thebest part of the most linear portion of the characteristic of eachstage, switch 64ar'1d key 65 may be closed to apply a high frequencywave from source 66 to the primary winding of transformer 67, thesecondary winding of which is connected through switch 64 with the inputterminals 50 of the receivingcircuit. When one or more of the tubes areso adjusted as to distort, the closure of key 65 causes a change in thedirect current transmitted through ammeter 19, power tube 40 producingthe greatest change, while low frequency amplifier 39 and the prioramplifier stages produce smaller changes when out of adjustment.

By adjusting the resistance connected with terminal 30, the negativepolarizing voltagev supplied to the grid of power tube 40 may be varieduntil the distortion produced in the tube is reduced to a minimum asindicated by the change of deflection of ammeter 19. IVhile the amountof distortion may be more conveniently adjusted for many purposes bymeans of variations in the resistance connected with terminal 30, it iswithin the scope of the present invention to adjust the resistanceconnected with the positive space current terminal 22, either inconjunction with or independently of an adjustment of the resistance inthe grid circuit. In some cases, where the observable distortion is veryslight, the grid voltage may be adjusted first to an extreme distortingvalue on one side of the minimum distorting value and then to an e uallydistorting value on the opposite side of the minimum, the adjustment forminimum distortion being then located between these extremes.- It willbe noted that the change .of deflection of the ammeter produced bydistortion in a repeater tube, is made apparent by intermittent closureof key 65.

be adjusted to the most linear working portion of its amplifyingcharacteristic, the next prior stages bem successively adjusted in theinverse order 0 their sequence'in the am lifier. Switch 64 may then beopened an keys 18 and 65 restored to normal so that the am lifier mathen 0 erate with a minimum o distortion. While adjusting the distortionto a minimum, the effect on ammeter 19 of distortion in detector 38 maybe avoided by energizing the anode circuit of the detector from a sourceof s ace current separate from the electric supp y unit.

The condensers in banks 27 and 33 improve the qualit of transmission ofthe amplified waves and provide paths of suitably low impedance for thealternating components of the current transmitted to and from theamplifier and detector tubes. Furthermore, each condenser in combinationwith the re; sistance unit associated therewith forms a filter sectionsupplementing the effect of filter 12 in sup ressing alternatmcomponents of current rom rectifier 7. y making condenser 28 of extralarge capacity, the impedance thereof is very small or negligible inrelation to the impedance of the output circuit connected with poweramplifier 40 or the last stage of the amplifier with which the condenseris connected.

I claim:

In a space current supply system, a direct current source having apositive terminal and a negative terminal, a bank of resistance unitshaving a common connection with the positive terminal for separatelycontrolling the voltages at said resistance units, a space currentreturn terminal, a main resistance unit connected between the negativeterminal of the direct current source and the space current returnterminal, and an additional ank of resistance units havin a commonterminal connected to the negative terminal of the direct currentsource, each unit in said additional bank bein separate from theother-units in said ban except at said common terminal, and each havinga free terminal for separately controlling an auxiliary potential.

In witness whereof I hereunto subscribe my name this 26th day of Au st,1926.

4 LOUIS G. ILLOT TE.

After adjusting the distortion of amplifier I 40 to a minimum ornegligible value, the next 65 prior amplifying stage including tube 39,may

